Growth in Britain’s construction firms fell unexpectedly to a one-year low in August, hit by an investment slump in the commercial sector as Brexit uncertainty weighed on the economy.

Countering more upbeat news about the economy last week, the Markit/CIPS Construction Purchasing Managers’ Index (PMI) fell to 51.1 from 51.9 in July, closer to the 50 mark that indicates stagnation. A poll of economists had expected a reading of 52.0.

Monday’s PMI underlined the uncertain outlook for an economy that has become increasingly difficult for the Bank of England to gauge.

A similar survey of manufacturers published on Friday had hinted at a strengthening of economic growth in the second half of the year.

Britain’s economy had its slowest first half of the year since 2012 as households came under pressure from a big rise in inflation following the fall in sterling caused by last year’s Brexit vote.

So far, construction, manufacturing and exports have failed to compensate for the consumer slowdown.

Construction makes up around 6 percent of British economic output. The Markit/CIPS survey for the much larger services sector – which accounts for nearly 80 percent – is due at 0930 GMT tomorrow.